/*
 * 参考 drivers\net\cs89x0.c
 */
static struct net_device *vnet_dev;


static void emulator_rx_packet(struct sk_buff *skb, struct net_device *dev)
{
	/* 参考LDD3 */
	unsigned char *type;
	struct iphdr *ih;
	__be32 *saddr, *daddr, tmp;
	unsigned char  tmp_dev_addr[ETH_ALEN];
	struct ethhdr *ethhdr;

	struct sk_buff *rx_skb;

	// 从硬件读出/保存数据
	/* 对调"源/目的"的mac地址 */
	ethhdr = (struct ethhdr *)skb->data;
	memcpy(tmp_dev_addr, ethhdr->h_dest, ETH_ALEN);
	memcpy(ethhdr->h_dest, ethhdr->h_source, ETH_ALEN);
	memcpy(ethhdr->h_source, tmp_dev_addr, ETH_ALEN);


	/* 对调"源/目的"的ip地址 */    
	ih = (struct iphdr *)(skb->data + sizeof(struct ethhdr));
	saddr = &ih->saddr;
	daddr = &ih->daddr;


	tmp = *saddr;
	*saddr = *daddr;
	*daddr = tmp;

	//((u8 *)saddr)[2] ^= 1; /* change the third octet (class C) */
	//((u8 *)daddr)[2] ^= 1;
	type = skb->data + sizeof(struct ethhdr) + sizeof(struct iphdr);
	//printk("tx package type = %02x\n", *type);
	// 修改类型, 原来0x8表示ping
	*type = 0; /* 0表示reply */

	ih->check = 0;  /* and rebuild the checksum (ip needs it) */
	ih->check = ip_fast_csum((unsigned char *)ih,ih->ihl);

	// 构造一个sk_buff
	rx_skb = dev_alloc_skb(skb->len + 2);
	skb_reserve(rx_skb, 2); /* align IP on 16B boundary */
	memcpy(skb_put(rx_skb, skb->len), skb->data, skb->len);


	/* Write metadata, and then pass to the receive level */
	rx_skb->dev = dev;
	rx_skb->protocol = eth_type_trans(rx_skb, dev);
	rx_skb->ip_summed = CHECKSUM_UNNECESSARY; /* don't check it */
	dev->stats.rx_packets++;
	dev->stats.rx_bytes += skb->len;


	// 提交sk_buff
	netif_rx(rx_skb);
}

static int virt_net_send_packet(struct sk_buff *skb, struct net_device *dev)
{
	static int cnt = 0;
	printk("virt_net_send_packet cnt = %d\n", ++cnt);


	/* 对于真实的网卡, 把skb里的数据通过网卡发送出去 */
	netif_stop_queue(dev); /* 停止该网卡的队列 */
		/* ...... */           /* 把skb的数据写入网卡 */


	/* 构造一个假的sk_buff,上报 */
	emulator_rx_packet(skb, dev);

	dev_kfree_skb (skb);   /* 释放skb */
	netif_wake_queue(dev); /* 数据全部发送出去后,唤醒网卡的队列 */

	/* 更新统计信息 */
	dev->stats.tx_packets++;
	dev->stats.tx_bytes += skb->len;

	return 0;
}

static int virt_net_init(void)
{
	/* 1. 分配一个net_device结构体 */
	vnet_dev = alloc_netdev(0, "vnet%d", ether_setup);;  /* alloc_etherdev */

	/* 2. 设置 */
	vnet_dev->hard_start_xmit = virt_net_send_packet;

	/* 设置MAC地址 */
    vnet_dev->dev_addr[0] = 0x08;
    vnet_dev->dev_addr[1] = 0x89;
    vnet_dev->dev_addr[2] = 0x89;
    vnet_dev->dev_addr[3] = 0x89;
    vnet_dev->dev_addr[4] = 0x89;
    vnet_dev->dev_addr[5] = 0x11;


   /* 设置下面两项才能ping通 */
	vnet_dev->flags           |= IFF_NOARP;
	vnet_dev->features        |= NETIF_F_NO_CSUM;


	/* 3. 注册 */
	//register_netdevice(vnet_dev);
	register_netdev(vnet_dev);

return 0;
}

static void virt_net_exit(void)
{
	unregister_netdev(vnet_dev);
	free_netdev(vnet_dev);
}
